Abstract: A system for obtaining an optimum focusing position in an optical disc system. An optical beam is impinged onto a track of an optical disc, and a reflection signal having information regarding an intensity of an optical beam reflected by an optical disc is obtained. A predetermined frequency component, the frequency component being generated by a modulation caused by an existence of a pit on a track of the optical disc in a reflecting signal, is extracted from the reflection signal. Then a focus position in which a maximum intensity of the extracted frequency component is obtained is searched by changing the focus position of the optical beam. Further, the above system is incorporated in a focus servo control system for maintaining an optimum focusing position in an optical disc system during reading and writing operations, to determine an optimum offset value which is to be adjusted to compensate an error arisen from a construction of the focus servo control system, during an offset adjusting operation.

Abstract: A fine access method for an optical disk drive uses a multi-track jump method to cover a wide range of several hundred tracks at a high speed. According to the present invention, one-shot acceleration and deceleration pulses with a short width are sent to an actuator head immediately after every one-half track pitch travel of the actuator head. The actuator head is accelerated when the travel time for one-half track pitch is slower than a first reference time and it is decelerated when the travel time is faster than a second reference time. When the travel time is between the first and second reference times, no pulse is sent to the actuator head. Thus the velocity of the actuator head is compensated and maintained within a specified range of deviation for a whole long range of jumping a plurality of tracks.

Abstract: A focusing and tracking servo system for generating focusing and tracking error signals for use in driving a servo system which focuses and tracks an optical beam, such as a laser beam on an optical disk. The system includes a photosensor having two sub-photosensors arranged to be adjacent to each other and to have a common boundary, and the laser beam has a circular cross-section and an optical axis. The laser beam reflected by the optical disk is incident on the photosensor so that the optical axis is offset from the boundary between the sub-photosensors. Consequently, the optical spot formed on each sub-photosensor has a different area and the sub-photosensors generate different photoelectric currents.

Abstract: A push-pull type tracking error signal produced by reflected light from pits on an ID area of an optical disk is averaged and sampled during a period while a light spot is scanned over the ID areas. An averaged value of a signal representative of the reflected light is stored for each sector of the disk, this value being a first sampled tracking error signal. The tracking error signal is also sampled while the light spot is scanned over a vacant zone having no pits in a data area, storing a second sampled tracking error signal. This vacant zone to be sampled is located either before or after a sequence of data bits in each sector. The first sampled tracking error signal is smaller than the second sampled tracking error signal because of the AC component produced by the pits. Thus, when an offset of the tracking exists, though the tracking error signal is kept almost zero by the servo control, the first sampled tracking error signal is not zero.

Abstract: An optical storage apparatus for storing and reading information on an optical disk with an optical beam, including a tracking servo system having an objective lens, which is driven in a focusing direction F and a tracking direction T by a lens actuator, and a tilting mirror, which is rotated by a mirror actuator. The tracking servo system eliminates beam shift by controlling the lens actuator and the mirror actuator to position the lens and the mirror so that the laser beam always passes through a back focal point of the lens located on the opposite side of the lens from the optical disk. As a result, the laser beam proceeds from the lens to the disk along a path which is parallel with the optical axis of the lens and strikes the disk perpendicularly. Accordingly, the return path of the laser beam reflected by the surface of the disk coincides with the incident path of the laser beam, and no beam shaft is experienced.

Abstract: A tracking servo apparatus for controlling a position of a light beam to follow an information track on an information storage disk. In response to a drive signal, a light-deflection mechanism moves the light beam onto the disk transversely with respect to the information track. The photodetector detects the difference in the intensity of the light beam in half sections and produces a radial error signal. The radial error signal is corrected in response to the drive signal which is applied to the light-deflection mechanism, and then a new drive signal is produced depending upon the corrected radial error signal.

Abstract: Semipermeable membranes useful in reverse osmosis and a process of preparing them comprising deacetylating naturally occurring chitin to produce chitosan, making a film of chitosan salt from an acid diluted aqueous solution of the chitosan, converting the film of chitosan salt to a film of chitosan having free amino groups by neutralizing the acid groups, and then subjecting the film of chitosan to a chemical treatment with an organic acid, by which to convert the chitosan to the acetylated form, having a degree of acetylation from about 0.3 to 0.8, to produce the reverse osmotic membranes.The products have excellent chemical properties as well as mechanical strengths sufficient to withstand the pressure difference in the operating condition.

Abstract: Unreacted monomer or monomers and any other volatile organic compounds contained in an aqueous dispersion of polymerizate are removed or separated by a method comprising circulating the aqueous polymerizate dispersion from the bottom of its container to the upper part of the container located over the surface of the dispersion via an exterior conduit. The pressure in the container is maintained at a level reduced to about the saturated vapor pressure of water at the temperature of the dispersion. This manner of separation of monomer from polymer serves to improve the working environment as well as the resulting polymer quality, and the monomer or monomers thus recoverd can be advantageously recycled.